A significant portion of the instant coffee market is decaffeinated instant coffee products. Several technical factors are important in the processing to form such coffee products. One factor is the effectiveness of the decaffeination process in removing caffeine from the coffee. A satisfactory process usually removes 97% or more of the caffeine from the coffee. Another factor is the efficiency of the decaffeination process in removing caffeine from the coffee. A process which is slower in decaffeinating coffee usually necessitates a large amount of capital equipment to handle commercial quantities of coffee.
The above technical factors further impact on the commercial acceptability of the decaffeination process. The decaffeination process should be economical. Factors which favor reduction in cost such as recovery of caffeine removed from the coffee are thus desirable. The decaffeination process should also provide a decaffeinated instant coffee product having a desirable flavor and aroma in terms of both quantity and quality. The quantity aspect relates to the total coffee solubles yield which can be extremely important to the cost effectiveness of the decaffeination process. The quality aspect relates to the retention of the key components which provide the aroma and flavor character of the coffee.
One method for forming decaffeinated instant coffee products involves green bean decaffeination. In one such process, green beans are prewet to increase the moisture content to upwards of 40% or more. The prewetted beans are then extracted with a water-immiscible organic solvent in a countercurrent fashion somewhat similar to that used to form coffee extract from roast and ground coffee. After decaffeination, the residual solvent is removed from the beans (desolventizing), usually by steam stripping. See U.S. Pat. No. 3,671,262 to Wolfson et al, issued June 20, 1972, and U.S. Pat. No. 3,671,263 to Patel et al, issued June 20, 1972. After stripping, the decaffeinated beans are roasted, ground and extracted as in a normal instant coffee processing system. See also U.S. Pat. No. 2,309,092 to Berry et al, issued Jan. 26, 1943, which discloses a related decaffeination process involving the formation of an aqueous extract of green coffee solubles which is decaffeinated with a water-immiscible organic solvent.
Green bean decaffeination methods are usually quite effective to remove caffeine from the coffee. However, such methods also have reduced processing efficiency. Whether the caffeine solvent is water or water-immiscible organic solvent, the mass transport mechanism for removal of caffeine from the beans is very slow. The decaffeination step usually requires several hours in order to provide effective decaffeination of the green bean. A similar statement can be made with regard to the step of desolventizing the decaffeinated beans. A green bean decaffeination process therefore more closely approximates a batch rather than a continuous decaffeination process.
Because of the reduced processing efficiency, green bean decaffeination methods can be relatively expensive. Such expense becomes especially great when commercial quantities of green coffee beans are involved. Because of the batch-like nature of the process, decaffeination of large quantities of beans increases the amount of capital equipment required, especially in the decaffeination and desolventizing steps. This capital equipment is typically quite costly. Also, a large storage and handling capacity is usually required at added cost.
There is some removal of coffee flavor and aroma compounds or precursors, especially water-insoluble waxes, during green bean decaffeination. These coffee compounds, as well as the caffeine, are desirably recovered to reduce the cost of the green bean decaffeination process and to improve the aroma and flavor quality of the decaffeinated instant coffee product. For example, solids present in the caffeine-containing organic solvent can be recovered by evaporating the solvent to dryness and extracting the solids with water. Oils and other insolubles can be separated for addback to the decaffeinated green beans. The residual aqueous phase can be concentrated and the caffeine crystallized for recovery. Alternatively, the caffeine-containing solvent can be contacted with water to recover the water solubles. The aqueous phase can then be extracted with additional caffeine solvent or evaporated to recover the caffeine. The water insolubles can be recovered from the original solvent by evaporation and/or subsequent treatment with water. See U.S. Pat. No. 3,669,679 to Panzer et al, issued June 13, 1972. See also U.S. Pat. No. 4,081,563 to Hudak et al, issued Mar. 28, 1978, wherein an aqueous extract from green coffee is dried, decaffeinated with a solvent such as ethyl acetate and the decaffeinated coffee solubles added back to the green coffee; coffee solubles present in the caffeine-rich solvent can also be recovered and added back to the decaffeinated coffee solubles.
Another method for forming decaffeinated instant coffee involves direct decaffeination of roast and ground coffee extract with a water-immiscible organic solvent. Such a decaffeination process is normally referred to as liquid-liquid extraction. In such a decaffeination process, roast and ground coffee extract is normally flowed countercurrently to the organic solvent. The solvent removes the caffeine from the coffee extract to provide a decaffeinated extract. The decaffeinated extract is stripped of residual solvent and then processed further to form a decaffeinated instant coffee product. See U.S. Pat. No. 2,933,395 to Adler et al, issued Apr. 19, 1960, which discloses a countercurrent extract decaffeination process.
Direct decaffeination of roast and ground coffee extract can be an effective and efficient method for removing caffeine from the coffee. For example, in countercurrent extract decaffeination, the coffee extract is usually dispersed in the form of small droplets through a continuous solvent phase. The small droplets present a large surface area to the solvent. Because of the large surface area, mass transfer of caffeine from the coffee extract to the solvent is significantly increased. Because of the increased mass transfer, extract decaffeination can become a truly continuous decaffeination process.
Direct decaffeination of roast and ground coffee extract can provide a less expensive decaffeination process than green bean decaffeination. The continuous nature of extract decaffeination can decrease capital equipment requirements for processing large quantities of coffee. Also, because coffee extract rather than green beans are decaffeinated, an extract decaffeination process requires less coffee bean inventory and is more flexible.
As with green bean decaffeination, the cost of an extract decaffeination process can be reduced by recovery of the caffeine. One such caffeine recovery system is disclosed in U.S. Pat. No. 2,508,545 to Shuman, issued May 23, 1950. Referring to the drawing of the Shuman patent, roast and ground coffee extract is decaffeinated in a liquid-liquid extraction column 2 with a suitable caffeine solvent such as trichlorethylene. The caffeine in the solvent is partitioned into an aqueous solution by liquid-liquid extraction. The caffeine-containing solution is concentrated at 5 to about 30% caffeine content and is then treated with carbon at 6 and 7. Alkali is added subsequent to carbon treatment to raise the pH to at least 7. The alkaline solution is water cooled and the caffeine crystallized out at 8. The crystallized caffeine is separated from the mother liquor by a centrifuge 9.
The Shuman patent indicates three different paths for further processing of the mother liquor. The first path involves return of the mother liquid to the caffeine-containing solution at 5. The second path involves concentration at 16 to about 30% caffeine content, crystallization of the caffeine at 17 and separation of the caffeine by centrifuge 18 with the residual mother liquor being discarded. The third path involves adding sulfuric acid at 20 with subsequent liquid-liquid extraction at 2A with a caffeine solvent such as trichlorethylene. The caffeine-containing solvent at 2A is combined with the caffeine-containing solvent from column 2. The residual mother liquor is discarded.
Another method for recovering caffeine obtained during decaffeination of roast and ground coffee extract is disclosed in U.S. Pat. No. 2,472,881 to Bender, issued June 14, 1949. Referring to the drawing of the Bender patent, the caffeine-containing solvent (e.g. trichloroethylene) is concentrated and then liquid-liquid extracted with water at 2. The decaffeinated solvent is recovered by evaporation at 4 with the residual water insoluble impurities being discarded. The aqueous caffeine solution which also has water soluble impurities is concentrated at 3, treated with carbon at 5 and 6 and the caffeine crystallized at 7. The crystallized caffeine is separated by a centrifuge 8 with the mother liquor ultimately liquid-liquid extracted with fresh organic solvent at 11. This caffeine-containing solvent from 11 is returned for further concentration at 1. The spent mother liquor containing water soluble impurities is discarded.
One significant problem with extract decaffeination is the loss of coffee flavor and aroma components, especially where less selective organic solvents such as ethyl acetate are utilized. An extract decaffeination process typically reduces the total coffee solubles yield. For example, after extract decaffeination, it has been found that a less selective organic solvent such as ethyl acetate contains a mixture of coffee solids, liquids and hard to define amorphous materials (hereinafter noncaffeine solubles) typically in a ratio to caffeine of approximately 2:1 by weight. These noncaffeine solubles also contain some of the key aroma and flavor components found to be missing from decaffeinated instant coffee products.
Only recently has concern been directed at the recovery of these important noncaffeine solubles in an extract decaffeination process. One such process is described in Belgium Pat. No. 865,488 to Bolt et al, issued Oct. 2, 1978. In the Bolt et al patent, the organic caffeine-containing solvent is extracted with water to form a caffeine-containing aqueous phase and a decaffeinated solvent phase. The decaffeinated solvent phase is combined with the decaffeinated extract. Typically, this solvent/decaffeinated extract mixture is sent to a flash evaporator to remove some of the solvent. The partially desolventized mixture is then sent to an extract stripper to remove the remainder of the residual solvent. The desolventized decaffeinated extract is then processed further to provide a decaffeinated instant coffee product.
The aqueous caffeine-containing phase separated from the decaffeinated solvent phase in the process of the Bolt et al Patent Document is normally referred to as spent water. It has been found that this spent water also contains noncaffeine solubles. For ethyl acetate as the solvent, the ratio of noncaffeine solubles to caffeine is approximtely 1:1 by weight. As noted previously, the caffeine recovery systems of the Shuman and Bender patents treat these noncaffeine solubles as "impurities". These "impurities" are ultimately discarded by the systems of both the Shuman and Bender patents. However, it has been found that the recovery of these noncaffeine solubles can significantly increase the total yield of decaffeinated instant coffee. Further, it has been found that these noncaffeine solubles contain important flavor and aroma components which are normally absent from decaffeinated instant coffee products formed by an extract decaffeination process.
It is therefore an object of the present invention to decrease the cost of an extract decaffeination process.
It is another object of the present invention to recover important coffee aroma and flavor components normally lost in an extract decaffeination process.
It is a further object of the present invention to increase the total coffee solubles yield of an extract decaffeination process.
It is yet another object of the present invention to recover caffeine as valuable by-product from an extract decaffeination process.
It is yet a further object of the present invention to recover important noncaffeine solubles while at the same time recovering caffeine.
These and other objects of the present invention are disclosed hereinafter.